Beryllium and Other Trace Elements in Paragneisses and Anatectic Veins of the Ultrahigh-Temperature Napier Complex, Enderby Land, East Antarctica: the Role of Sapphirine |
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Authors: | GREW EDWARD S; YATES MARTIN G; SHEARER CHARLES K; HAGERTY JUSTIN J; SHERATON JOHN W; SANDIFORD MICHAEL |
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Institution: | 1 DEPARTMENT OF EARTH SCIENCES, UNIVERSITY OF MAINE, 5790 EDWARD T. BRYAND RESEARCH CENTER, ORONO, ME 04469-5790, USA
2 INSTITUTE OF METEORITICS, UNIVERSITY OF NEW MEXICO, ALBUQUERQUE, NM 87131, USA
3 STONEACRE, BREAM ROAD, ST. BRIAVELS, LYDNEY GL15 6TL UK
4 SCHOOL OF EARTH SCIENCES, UNIVERSITY OF MELBOURNE, CARLTON, VIC. 3010, AUSTRALIA |
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Abstract: | Anatectic veins containing the Be minerals khmaralite and berylliansapphirine as primary phases (or surinamite derived therefrom)are associated with MgAl-rich paragneisses at three localitiesin the ultrahigh-temperature Napier complex, Antarctica, a uniqueBe mineralization in the granulite facies. Likely precursorsof the paragneisses are volcaniclastic deposits that were hydrothermallyaltered by heated seawater prior to metamorphism. Regular distributionof Be among minerals in the paragneisses suggests an approachto equilibrium with Be greatly concentrated in sapphirine (253430ppm Be) or cordierite (560930 ppm Be) relative to plagioclaseAn5366 (1443 ppm Be) > cores of coarse-grainedorthopyroxene (0·729 ppm Be) > coronitic orthopyroxene(0·414 ppm Be) sillimanite (0·126ppm Be) plagioclase An1833 (0·615 ppmBe) > biotite (0·068 ppm Be) > K-feldspar,quartz, garnet (0·050·7 ppm Be). Sapphirine-bearingparagneisses have average Be concentrations, 4·9 ±2·4 ppm (13 samples), about twice that of typical pelites,whereas paragneisses lacking sapphirine and primary cordieritehave only 2·9 ± 2·1 ppm Be (12 samples),implying some loss of Be during metamorphism. The likely sourcerocks for the Be-rich melts were biotitic rocks lacking theBe sinks sapphirine and cordierite. These gneisses were probablyless competent than the sapphirine-bearing gneisses, so themelts were drawn to the latter and collected in spaces openedduring deformation and boudinage of the more competent paragneisses.Fractionation of the melts concentrated Be to the extent thatBe minerals could crystallize. The final result was Be-mineralizedanatectic veins hosted by relatively Be-rich sapphirine-bearingparagneisses. KEY WORDS: Antarctica; beryllium; granulite facies; microprobe; sapphirine |
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Keywords: | : Antarctica beryllium granulite facies microprobe sapphirine |
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